The present invention relates generally to pumps, and more particularly to a pump piston assembly and to a pump piston assembly.
Conventional pumps include pumps for vehicle control braking systems which perform anti-lock braking, stability enhancement, and traction control. In one conventional pump design, the pump includes a pump sleeve and a pump piston assembly. The pump sleeve has opposing first and second sleeve ends and has a sleeve bore extending from the second sleeve end toward the first sleeve end. The pump piston assembly has a pump piston, a pump check valve, a spring, and a spring retainer. The pump piston has opposing first and second piston ends and has a piston bore extending from the first piston end toward the second piston end. The pump piston is slidably engaged in the sleeve bore. The first piston end is located inside the sleeve bore, and the second piston end is located outside the sleeve bore. The second sleeve end is located between the first and second piston ends. The pump check valve is positioned proximate the first piston end. The spring is a cylindrical coil spring having a first spring end in contact with the inlet check valve and having a second spring end extending longitudinally away from piston. A spring retainer has one end attached (by a crimp or a press fit) to the first piston end and has another end which extends longitudinally away from the piston and which surrounds and retains the second spring end. The pump has a volumetric compression ratio equal to the ratio of the pumping chamber volume at the full piston withdrawal position to the pumping chamber volume at the full piston insertion position.
What is needed is a pump and a pump piston assembly, such as for a vehicle control braking system, which has a higher volumetric compression ratio.
In a first expression of a first embodiment of the invention, a pump piston assembly includes a pump piston, a pump check valve, and a spring. The pump piston has opposing first and second piston ends and has a piston bore extending from the first piston end toward the second piston end. The pump check valve is positioned proximate the first piston end. The spring has an attached portion attached to the pump piston proximate the first piston end and has a biasing portion biasing the pump check valve to fluidly block the piston bore. The attached portion of the spring is closer to the second piston end of the pump piston than is the biasing portion of the spring.
In a second expression of a first embodiment of the invention, a pump includes a pump sleeve and a pump piston assembly. The pump sleeve has opposing first and second sleeve ends and has a sleeve bore extending from the second sleeve end toward the first sleeve end. The pump piston assembly has a pump piston, a pump check valve, and a spring. The pump piston has opposing first and second piston ends and has a piston bore extending from the first piston end toward the second piston end. The pump piston is slidably engaged in the sleeve bore. The first piston end is positioned inside the sleeve bore, the second piston end is positioned outside the sleeve bore, and the second sleeve end is located between the first and second piston ends. The pump check valve is positioned proximate the first piston end. The spring has an attached portion attached to the pump piston proximate the first piston end and has a biasing portion biasing the pump check valve to fluidly block the piston bore. The attached portion of the spring is closer to the second piston end of the pump piston than is the biasing portion of the spring.
Several benefits and advantages are derived from the invention. The invention eliminates the protruding spring retainer of the prior art, and the spring of the invention extends back over the check valve to the piston instead of protruding beyond the check valve and the piston as in the prior art. This allows a smaller size and less expensive pump piston assembly and hence a smaller size and less expensive pump. Also, eliminating the protruding spring retainer and extending the spring back over the check valve allows a smaller volume in the pumping chamber (the region between the check valve and the bottom of the sleeve bore) at the full piston insertion position. This increases the pump volumetric compression ratio (the ratio of the pumping chamber volume at the full piston withdrawal position to the pumping chamber volume at the full piston insertion position). Increasing the pump volumetric compression ratio increases the efficiency of the pump which, for example, makes the pump more tolerant of air entrained in brake fluid when the pump is used in a controlled breaking system of a vehicle.